In my opinion, there are far too many myths circulating the internet that aquarium fish can live without a filter. Although very advanced aquarists have occasionally managed to create densely planted filterless tanks, these complex setups are unsuitable for the vast majority of fish keepers.
For the rest of us, an aquarium filter is an essential piece of kit, and without one, fish and invertebrates die very quickly. Here we’ll look at some types of fish that, in emergencies, can live without a filter for a longer time than others.
Just promise me you won’t try to keep them like that for the long run!
Key Takeaways
- The vast majority of fish keepers need an aquarium filter to keep the water clean, well-oxygenated, and free from toxins.
- Without a filter, fish will quickly die from ammonia poisoning or oxygen depletion. Some fish families such as labyrinth fish, catfish, and danios, however, can live longer like this than others.
- Aquarium filters are cheap, easy to operate, and will save you a lot of time changing water. Choosing a setup without a heater is more cost-effective than a filterless aquarium.
Betta Fish
- Scientific Name: Betta splendens
- Adult Size: 3 inches
- Life Expectancy: 2 to 3 years
The infamous betta fish or Siamese fighting fish is sometimes listed as a species that can live without a filter. But while a betta may be able to survive in a tank or bowl without a filter for a short time, it definitely won’t thrive.
Sadly, bettas kept in poor water conditions will often die before their first birthday – tragic for a beautiful fish that can exceed 5 years in a well-maintained aquarium!
The reason that betta fish are hardier than most is the adaptations they’ve made to their natural habitat. In the wild, bettas are found in shallow pools, swamps, and rice paddies, which can become low in oxygen.
To survive such conditions, bettas have evolved a special organ known as the labyrinth organ which allows them to breathe some of their oxygen from the air as well as the water.
As we’ve said, this mustn’t be taken as a reason to keep bettas in poor water conditions, and their sensitivity to ammonia and other toxins means that a filter is still essential except in emergencies!
Guppies
- Scientific Name: Poecilia reticulata
- Adult Size: 2 inches
- Life Expectancy: 2 to 3 years
The poor guppy is the victim of a lot of mistreatment in the pet trade, partly owing to their prolific rate of breeding and the very cheap price you pay for them – they’re sometimes seen as expendable. But we must remember that the guppy is an intelligent fish species like any other. If you can become sentimental about your favorite clown loach or angelfish, then why not your guppy?!
Guppies are hardy fish that can tolerate an extraordinarily wide range of temperatures, but their tolerance for poor water conditions might not be as endless as you imagine. As active fish, they require decent oxygen levels and can suffer ammonia poisoning just like any other species.
So, remember, they’re likely to survive longer than some other fish, but you’ll still need to clean your filter and change your water often to keep them alive and well.
Goldfish
- Scientific Name: Carassius auratus
- Adult Size: 12 to 14 inches
- Life Expectancy: 15 to 20 years
The goldfish is another fish that often suffers because of its robust reputation. But just because goldfish have been kept in bowls without a filter, doesn’t mean they’re happiest that way.
Goldfish are heavy feeders and produce a high bio load, meaning that if you keep them without a filter, you’ll need to change half of their water every day!
While some sources have listed goldfish as a labyrinth fish that can breathe oxygen from the air, this is not true! Like most fish, goldfish can only breathe oxygen that’s been dissolved in the water through their gills.
The real reason that goldfish are good at surviving low oxygen levels is their physical adaptation to suppress metabolism when exposed to poor water conditions.
Funnily enough, the primary organ that they sacrifice to save oxygen is their brain! Maybe it’s why goldfish famously fail the memory test.
Corydoras Catfish
- Scientific Name: Corydoras
- Adult Size: 2-3 inches
- Life Expectancy: 5 to 10 years
Corydoras catfish, affectionately known as ‘corys’, are a popular family of catfish for freshwater aquariums. Popular species include the Bronze cory, Panda cory, and pygmy cory.
These bottom feeders do a fantastic job of keeping the tank clean by constantly rooting around in the substrate, looking for algae and food that would otherwise rot and pollute the tank.
In this way, corys do you a favor by supplementing the work of an aquarium filter. But can corys live for long without a filter?
Like betta fish, cory catfish have specialized breathing apparatus that allows them to breathe oxygen from the air as well as water. If you’ve ever seen your cory hurtling towards the surface to gulp a breath of air, it might mean your tank was low in oxygen.
When my peppered corydoras used to do this, he’d make me laugh – they always look like they’re in such a hurry. I didn’t realize until later that the speed at which they jet to the surface and back again is a behavioral adaptation to keep them safe. Swimming to the surface can be dangerous for such a small fish, so they need to do it as quickly as possible to avoid being eaten by a larger fish!
Gouramis
- Scientific Name: Helostomatidae
- Adult Size: 3-12 inches
- Life Expectancy: 5-25 years
Gouramis are a popular family of tropical fish that hail from India, China, and down to Indonesia.
Popular species include the Dwarf gourami, Pearl gourami, and Moonlight gourami. Like betta fish, gouramis are labyrinth fish, meaning they can breathe oxygen from the air as well as water.
This gives them a real advantage when living in low-oxygen environments, like the shallow pools that they come from in Asia. Because of this remarkable adaptation, gouramis might live longer than some other fish without a filter.
Gouramis shouldn’t be neglected though, and in the long term will definitely need a filter. If you take good care of your aquarium water quality and feeding regime, some gourami species can live for more than 20 years!
Zebra Danios
- Scientific Name: Danio rerio
- Adult Size: 2 inches
- Life Expectancy: 5 years
When we’re looking at hardy aquarium fish species, Zebra danios or ‘zebra fish’ are about as tough as they come. This fish can tolerate an astonishing range of temperatures, right the way from 45°F – 118°F, which is pretty exceptional for any fish species.
This means Zebra danios are quite comfortable living without a heater, but for how long can they live without a filter?
These small fish are easy to care for and don’t create much of a bio-load, so won’t dirty their water or create a lot of ammonia in a short space of time. They are, however, very active fish and need a plentiful oxygen supply to keep them healthy.
If you somehow find yourself temporarily without a filter, be sure to make partial water changes daily to keep your zebra fish with a plentiful source of oxygen.
Paradise Fish
- Scientific Name: Macropodus opercularis
- Adult Size: 4 inches
- Life Expectancy: 6 to 8 years
Like gouramis and bettas, paradise fish are part of the Anabantoidei family that possess a labyrinth organ. This means that like its cousins, the paradise fish possesses the superpower to breathe oxygen from the air as well as the water.
Paradise fish were one of the first exotic fish to be imported to Europe for the aquarium trade, and they made a good choice for a couple of reasons: they’re very beautiful and relatively hardy.
Paradise fish can tolerate a wider range of water conditions than many other fish. They’re not too fussy about water pH or hardness, and can even tolerate temperatures down to 65 Fahrenheit.
Their hardiness means you could keep a paradise fish successfully without a heater, and their ability to breathe air might also help them survive longer than other fish without a filter. Ammonia, however, would quickly become a problem unless you changed the water every day.
Japanese Rice Fish
- Scientific Name: Oryzias latipes
- Adult Size: 1.5 inches
- Life Expectancy: 3-4 years
Japanese rice fish are energetic little critters who love to zoom around the aquarium night and day. Being from Japan, they’re more cold-hardy than fish species from more tropical regions and prefer to be kept in cold-water aquariums.
The name ‘rice fish’ also tells us exactly where this fish likes to live in their native lands! Like betta fish and gouramis, Japanese rice fish like to hang out among rice paddies – essentially fields of rice that are temporarily flooded with shallow water.
These conditions in the rice paddies are quite challenging for fish, with the water being rather cloudy and low in oxygen. So if a fish can survive there, they’ll likely be able to live without a filter for a longer time than fish that come from crystal clear waters.
Cold water is also naturally richer in oxygen than warm water, which can help cold-water fish live without additional oxygen for longer periods than most tropical fish.
Freshwater Shrimp
- Scientific Name: Caridea
- Adult Size: 1 – 10 inches
- Life Expectancy: 1-12 years
Aquarium shrimps such as ghost shrimp, cherry shrimp, and Amano shrimp are some of the easiest aquatic pets to keep. They’re normally peaceful, undemanding, and easygoing characters, and also do an excellent job at helping to keep your fish tank clean.
Some people have tried keeping shrimps in a planted fish bowl without a filter, and they may survive this treatment for short periods.
For the long term, however, keeping shrimp without a filter is not such a good idea. Just like fish, shrimp need a plentiful supply of oxygen, and without it, you might see them dashing to the surface to breathe from the surface layer of water. If you fail to replenish their oxygen supplies when they give you this sign, they’ll likely soon die.
Shrimp are also sensitive to nitrite and ammonia, which will build up in their tank or bowl without a filter. Without a filter, you’d need to provide your shrimps with daily water changes to ensure enough oxygen and safe water conditions.
Pond Snails
- Scientific Name: Lymnaea stagnalis
- Adult Size: 0.5 inches
- Life Expectancy: 1-2 years
Pond snails are one of the few invertebrates that you really can keep in water with low oxygen levels. While most aquatic snails have gills and breathe underwater, pond snails have a primitive lung that allows them to breathe from the air.
This amazing adaptation that allows these snails to survive in water that’s very low in oxygen, could also, in some circumstances, help them survive without a filter.
These snails, however, are still sensitive to ammonia spikes and are even used by scientists as a bioindicator for water that’s contaminated. If they’re present and unharmed it means ammonia levels are not dangerously high.
On the plus side, pond snails are excellent at keeping your tank clean, and assist your filter in its work of improving water quality.
Good to know: Pond snails don’t tend to eat healthy live plants, but they can reproduce very quickly, meaning population explosions can be a problem.
Ramshorn Snails
- Scientific Name: Planorbidae
- Adult Size: 0.5 – 2 inches
- Life Expectancy: 1-2 years
Like pond snails, Ramshorn snails have a primitive lung, rather than gills for breathing, so can do well in tanks with low levels of dissolved oxygen.
But although these snails have beautiful, spiraling shells, they can also be a pest in the aquarium by devouring your precious live plants as well as the algae and detritus that you want them to eat! They can also breed very fast, so if you have living plants, it’s best to steer clear of these types of snails.
If you’re not planning on growing plants, however, the Ramshorn snail can be one of the hardiest aquatic pets you can imagine. Along with the pond snail, they could probably live in water without a filter longer than just about any other aquatic pet you could find.
4 Reasons Aquarium Filters Are Essential
In the list above, we discussed some of the species of fish and invertebrates that could survive without an aquarium filter for longer than most. But that doesn’t mean they’d be happy or healthy without one.
Aquarium filters perform many crucial roles in a fish tank, and here are a few of the reasons that it’s important to have one:
Filters Oxygenate the Tank’s Water
All animals, including fish, shrimp, amphibians, and snails need oxygen. While a few of these aquatic pets have a special ability to breathe oxygen from the air, they’ll be happier if there’s plenty of dissolved oxygen in the water, too.
By creating a water current, filters improve gas exchange at the water’s surface. The more that the surface water is moving, the more gas exchange takes place, and the more oxygen can be dissolved into the water.
Filters also remove rotting debris from the water which would otherwise consume a lot of oxygen through the process of decomposition.
Filters Remove Toxic Ammonia
Ammonia is one of the most toxic substances to fish, and it’s also a product of fish waste.
This means that if fish are kept in a captive environment without a filter or water changes, ammonia levels quickly build up and cause permanent damage or death to your fish.
Filters remove ammonia from the water by a remarkable process known as “biological filtration.” To put it simply, good bacteria colonize the filter’s media and convert toxic ammonia into less harmful nitrates. This is why every aquarium needs to go through an initiation process known as ‘cycling‘ while the beneficial bacteria populations build up enough to do their job properly before fish can be safely introduced.
Filters Save You a Lot of Time and Energy!
If you thought you could save yourself time by not having a filter, think again!
While you’ll only need to clean your filter’s sponges every two weeks or so, an aquarium without a filter will need to be manually cleaned every day!
If you neglect to do this daily cleaning and partial water changes, levels of ammonia will build up, oxygen levels will go down, and your fish will be at great risk of permanent damage or death.
Filters Are Easy To Use and Extremely Affordable
The final reason we’ll give to persuade you to get a filter is that they’re easy to operate and incredibly cheap.
While advanced canister filters could set you back several hundred dollars, a simple sponge filter with an air pump can be acquired for less than 20 bucks. Not much considering all the work they do for you!
Filters also are quite economical to run, sometimes consuming as little as 5 watts of electricity. This amounts to only around $10 per year!
If You Want To Save Money, Ditch Your Heater Before Your Filter!
If you’re looking to cut your spending costs on keeping fish, then consider a tank without an aquarium heater before cutting out your filter. Heaters cost more money to run than filters. Even a small one for a 10-gallon tank will consume 25 watts – between 3-5 times much more than a filter does.
Cold water fish tanks can still be interesting and beautiful, with a wide variety of plants and fish species suitable. Just from the list above, we can find goldfish, guppies, zebra danios, paradise fish, pond snails, ramshorn snails, and Japanese rice fish, all as suitable options for an aquarium without a heater.
Java fern, Java moss, various Anubias, and moss balls are all good plants for unheated tanks, too.
You can find out much more about the different types of filters and how they function in our dedicated 101 guide for aquarium filters.
